We plan to study sites of binding and mechanism of action or purified gonadotropins in rat and human testes. Purified luteinizing hormone (LH) and follicle stimulating hormone (FSH) will be radioiodinated and utilized 1) to identify receptors for each hormone and 2) to determine specificity of receptors for each hormone in isolated seminiferous tubles (rat and human) and interstital tissue (rat). The role of FSH and LH in synthesis and release of testosterone in rat and human testes will also be studied. Radioimmunoassay will be employed fo quantitation of testosterone and other androgens in incubation media and in tissues. The mechznism by which FSH and LH increase steroid sulfaatase activity and testosterone production in intact rat testes, isolated interstitial tissue and seminiferous tubules will be examined. Investigationswill be carried out to determine 1) whether effects of FSH or LH onsteroid sulfatase activity and testosterone production are mediatedbby cyclic AMP 2) whether either gonadotropin stimulated cyclic AMP synthesis in interstitial tissure or seminiferous tubules and 3) whether new RNA synthesis or protein synthesis is essential for the observed increase in steroid sulfatase activity and testosterone production.